High Repeatibility and Short Cycle Times are Key to Successful Vitamin Palletizing Operation

Problem:

BASF has the right formula ready, not only for manufacturing its vitamin A concentrate, but also for automated palletizing. In a single shift, and in a limited space, a six-axis KUKA robot handles sacks filled with vitamins with a cumulative weight of approximately 30 tons. A decisive role in this is played by the gripper system, which is exactly tailored to the application. The crucial factors favoring the robot were – besides the small floor space requirement – above all its high repeatability and flexibility and short cycle time. 

Solution:

BASF Aktiengesellschaft’s plant in Ludwigshafen, Germany, the birthplace and headquarters of the group, has in the course of more than 130 years developed into the world’s largest contiguous chemical plant array owned by a single company. Today, the plant is divided into 350 individual units, not to mention numerous laboratories. The plant’s other figures are similarly impressive: it consumes as much electricity as Denmark, and covers an area of 7.1 square kilometers. This territory, which extends along the banks of the Rhine for 7.5 km, is crisscrossed by 115 km of roads and 211 km of railroad tracks. About 2,000 km of aboveground pipelines are used for transporting basic chemical products.

BASF’s worldwide sales in 1998 totaled DM 54 billion. The company, which was founded in 1865, employs about 106,000 people worldwide, of which 44,000 work in Ludwigshafen alone. These are supplemented by some 6,000 permanent service workers.

“Besides enzymes, organic acids and amino acids, vitamins are an important product group of our company’s Fine Chemicals division”, emphasizes Dr. York Hartleben, who is responsible for vitamin formulation in BASF’s fine chemicals production. “Quantitively, most of our production is used in animal feed, however we are also suppliers to the foodstuffs and pharmaceutical industries”.

The robotic cell, which was set up by the KUKA systems partner Koch-Industrieanlagen GmbH from Dernbach near Dierdorf, is used to palletize sacks filled with vitamin A concentrate. For reasons of recycling, BASF uses bags made of PE with a layer of aluminum; since this is not a composite material, it is easy to recycle. When preparing shipments destined for overseas recipients, BASF in addition places the sack in a cardboard box for transport.

Switching to robotic palletizing was decided by the chemicals group to improve productivity and a more worker-friendly environment. The employees concerned are now working in other departments of the company. At the center of the automation is a KUKA KR 125 robot with a fork gripper for handling the sacks. The weight of the gripper and sack, requires that a carrying capacity of 125 kg payload is needed for smooth operation.

A decisive criterion in automating this process was the floor space requirement. The space available was relatively small, and the ceiling is not very high. During handling operations, only 3 cm remain between the top of the robot and the ceiling when the robot reaches its highest position.

“Originally we had planned to use a palletizing machine, which costs less and which up until now represented the standard solution for such applications. The major argument against this, however, was its height requirement, which would have necessitated constructing a pit. Besides the additional expense this would have involved, such a design would have been questionable from a food technology point of view, if only because of the difficulty and expense of cleaning”, explains Dr. Hartleben. “Additional arguments in favor of the robot were its short cycle time and good figures with respect to repeatability and flexibility”.

Repeatability is of particular significance, since precise stacking plays a large part in preventing transportation damage. Moreover, it was very important to BASF that the KR 125 (supplied by KUKA Roboter GmbH, based in Augsburg, Germany) be able to pick up and set down the sacks and boxes gently.

The user values the flexibility of the six-axis robot most of all for its ability to switch at any time between different container forms and stacking patterns. For example, the robot “knows” how to make composite stacks of sacks and column stacks of cardboard containers.  A vision system sends the robot this information and the robot can then adjust its position to accommodate the different container shapes.  Compared to a conventional palletizer, which sometimes actually has to be modified in the case of varying containers or conditions, with the KR 125 all one has to do is choose the appropriate program from those stored in the robot controller. To simplify this procedure even further, BASF had a lever installed which makes it even easier to select either one of the two standard programs, with practically no knowledge of the system on the part of the operator being required. Other programs are also provided, e.g. for varying the number of layers depending on the shipping order.
With regard to the cycle time, the robotic cell is designed for growth; a potential growth in capacity has already been provided for. At present, the KR 125 - with a cycle time of ten seconds - stacks approximately 30 tons of vitamins. For the more demandin shifts it is possible to implement a cycle times of seven to eight seconds. The gain in productivity from using a robotic cell can be assessed if one considers that palletizing one sack previously took a whole minute.

Vitamin A is automatically put into 25 kg sacks by two “form-fill-seal” machines. The first machine packages three brown sacks, and the second machine packages one white.  After passing through a weighing and labeling station, the sacks arrive at the robot on a conveyor belt. Also integrated into the robotic cell is a conveyor system leading away from the cell and the safety facilities.

Just before reaching the robot, the goods are transferred from the conveyor belt to a roller conveyor. This way the vision system can report to the KR 125 that a container has arrived, and the robot can reach between the rollers of the conveyor with the forks of its gripper, and lift the sack without damaging it. Then the robot gently stacks the bag on a pallet, which is located on the outgoing roller conveyor. After that, the fully-loaded carrier is placed on a rotating table, where an automatic wrapping machine encloses it in stretch foil. Finally, the pallet rolls to an end position, where it is removed by a fork lift. The robot can also handle cardboard boxes using the same fork gripper that is uses for the sacks.

The robotic cell has been in operation since December 1996; the preceding planning was completed on schedule in just over seven months. “A test setup at the system integrator’s plant validated the functions of the system right at the outset”, according to Dr. York Hartleben. “We liked the Koch company’s service – their presentation and commitment – since the goal was to use various tests to find the most economical concept. Thanks to this, a clear, valid solution was found very quickly.”

In addition, the fact that today BASF requires two fewer workers in palletizing means that the cell will have paid for itself in a relatively short time. The high availability of the robotic cell is also important here; BASF is reinforcing this by sending some of its own employees for training at the KUKA systems partner’s plant.

Author: Jürgen Warmbold, freelance technical journalist, 27327 Martfeld